Poultry Diseases MCQ: A Self-Assessment Tool for Veterinary Students and Practitioners

Introduction

Competency in poultry disease diagnosis requires integration of clinical signs, gross pathology, histopathology, and laboratory diagnostics. Multiple-choice questions (MCQs) serve as an effective self-assessment modality for veterinary students and practitioners to reinforce knowledge of etiology, pathogenesis, differential diagnosis, and control measures. This article presents a curated set of MCQs covering bacterial, viral, parasitic, and fungal diseases of poultry. Each question is followed by the correct answer and a brief explanation. The questions are designed to reflect common examination topics and practical diagnostic challenges encountered in commercial and backyard flocks.

The MCQs are organized by pathogen category. A decision tree for respiratory disease differential diagnosis is provided as a Mermaid diagram, and a summary table of key pathogens is included for rapid reference. Cross-references to relevant articles on this portal are provided where applicable.

Bacterial Diseases

Question 1
A broiler flock presents with sudden onset of lameness, swollen hocks, and pasty vents. Postmortem examination reveals fibrinous pericarditis and perihepatitis. Which bacterial pathogen is most likely responsible?
A. Mycoplasma gallisepticum
B. Avian Pathogenic Escherichia coli (APEC)
C. Clostridium perfringens type A
D. Pasteurella multocida

Answer: B
Explanation: Fibrinous pericarditis and perihepatitis (coligranuloma) are classic lesions of colibacillosis caused by APEC. Lameness and swollen joints may result from septic arthritis. Mycoplasma gallisepticum typically causes respiratory signs and airsacculitis. Clostridium perfringens type A is associated with necrotic enteritis. Pasteurella multocida causes avian cholera with septicemia and sudden death. For further details on APEC virulence factors and diagnostics, see Avian Pathogenic Escherichia coli (APEC): Virulence Factors, Rapid Diagnostic Assays, and Biosecurity Strategies.

Question 2
A flock of 6-week-old broilers exhibits increased mortality with dark red, friable intestines and a foul odor. Histopathology shows severe necrosis of the intestinal mucosa with large gram-positive rods. Which toxin is primarily responsible for the lesions?
A. Alpha toxin
B. NetB toxin
C. Heat-labile enterotoxin
D. Cytotoxic necrotizing factor

Answer: B
Explanation: Necrotic enteritis in broilers is primarily caused by Clostridium perfringens type A strains that produce NetB toxin. Alpha toxin (phospholipase C) contributes but NetB is the key virulence factor. Heat-labile enterotoxin is associated with enterotoxigenic E. coli. Cytotoxic necrotizing factor is produced by some E. coli strains. For a detailed review, see Necrotic Enteritis in Broiler Chickens: Clostridium perfringens Virulence Factors, Gut Microbiome, and Probiotic Control Strategies.

Question 3
Which of the following is the most reliable method for diagnosing Mycoplasma gallisepticum infection in a live chicken?
A. Tracheal swab culture on blood agar
B. Serum plate agglutination test
C. Real-time PCR targeting the 16S rRNA gene
D. Direct Gram stain of conjunctival swab

Answer: C
Explanation: Real-time PCR offers high sensitivity and specificity for M. gallisepticum detection from tracheal or choanal swabs. Culture is fastidious and slow. Serum plate agglutination can yield false positives due to cross-reactivity with M. synoviae. Gram stain is not useful for mycoplasmas as they lack a cell wall. For more on clinical presentation and molecular approaches, see Mycoplasma gallisepticum in Backyard Poultry: Clinical Presentation and Molecular Diagnostic Approaches.

Question 4
A waterfowl die-off occurs in a wetland area. Affected birds are found dead with no premonitory signs. Necropsy reveals petechial hemorrhages on the heart and liver. Pasteurella multocida is isolated. Which serotype is most commonly associated with avian cholera in waterfowl?
A. Serotype 1
B. Serotype 3
C. Serotype 4
D. Serotype 5

Answer: A
Explanation: Pasteurella multocida serotype 1 is the predominant serotype causing avian cholera in waterfowl. Serotypes 3 and 4 are more common in turkeys and chickens. Serotype 5 is occasionally isolated. For outbreak dynamics and vaccination, see Avian Cholera in Waterfowl: Pasteurella multocida Serotypes, Outbreak Dynamics, and Vaccination Approaches in Wild and Domestic Birds.

Question 5
A backyard flock of 20 chickens shows respiratory distress, facial edema, and purulent ocular discharge. Gram stain of exudate reveals gram-negative rods. Which pathogen is most likely?
A. Salmonella enterica serovar Typhimurium
B. Avibacterium paragallinarum
C. Gallibacterium anatis
D. Ornithobacterium rhinotracheale

Answer: B
Explanation: Avibacterium paragallinarum is the causative agent of infectious coryza, characterized by facial edema, nasal discharge, and conjunctivitis. Salmonella Typhimurium causes enteritis and septicemia. Gallibacterium anatis is an opportunistic pathogen. Ornithobacterium rhinotracheale causes respiratory disease but typically in turkeys and older chickens.

Viral Diseases

Question 6
A flock of 4-week-old broilers exhibits severe respiratory distress, cyanosis, and high mortality. Postmortem shows tracheal plugs and hemorrhagic tracheitis. Which virus is most likely?
A. Infectious bronchitis virus (IBV)
B. Newcastle disease virus (NDV)
C. Avian influenza virus (AIV)
D. Infectious laryngotracheitis virus (ILTV)

Answer: D
Explanation: ILTV (a herpesvirus) causes acute respiratory disease with hemorrhagic tracheitis and diphtheritic membranes. IBV causes tracheal ciliary loss but not hemorrhagic plugs. NDV and AIV can cause respiratory signs but hemorrhagic tracheitis is characteristic of ILTV. For molecular diagnostics of avian influenza, see Avian Influenza A(H5N1) in Poultry and Wild Birds: Current Epidemiology, Molecular Diagnostics, and Biosecurity.

Question 7
Which of the following viruses causes immunosuppression in young chickens by targeting B lymphocytes in the bursa of Fabricius?
A. Marek's disease virus (MDV)
B. Infectious bursal disease virus (IBDV)
C. Chicken anemia virus (CAV)
D. Fowlpox virus

Answer: B
Explanation: IBDV (a birnavirus) replicates in the bursa of Fabricius, causing necrosis of B lymphocytes and subsequent immunosuppression. MDV targets T lymphocytes. CAV causes anemia and immunosuppression but targets hematopoietic cells. Fowlpox virus causes cutaneous lesions. For variant strains, see Infectious Bursal Disease Virus Variants.

Question 8
A layer flock experiences a drop in egg production with misshapen, soft-shelled eggs. No respiratory signs are observed. Which virus is most likely?
A. Egg drop syndrome virus (EDS76)
B. Infectious bronchitis virus (IBV)
C. Newcastle disease virus (NDV)
D. Avian encephalomyelitis virus (AEV)

Answer: A
Explanation: EDS76 (an adenovirus) causes a sudden drop in egg production and poor eggshell quality without respiratory signs. IBV also affects egg quality but typically with respiratory signs. NDV causes respiratory and nervous signs. AEV causes neurological signs in young birds.

Question 9
Which of the following is a key feature of highly pathogenic avian influenza (HPAI) in chickens?
A. Mild respiratory signs only
B. Neurological signs and sudden death
C. Chronic respiratory disease with low mortality
D. Intestinal hemorrhage and diarrhea

Answer: B
Explanation: HPAI viruses (e.g., H5N1) cause systemic infection with neurological signs, edema of the head, and sudden death. Mild respiratory signs are typical of low pathogenicity avian influenza (LPAI). Intestinal hemorrhage is more characteristic of Newcastle disease.

Question 10
A 10-week-old turkey flock shows progressive paralysis and blindness. Gross lesions include enlarged nerves (brachial and sciatic plexi). Which virus is the cause?
A. Marek's disease virus (MDV)
B. Reticuloendotheliosis virus (REV)
C. Turkey herpesvirus (HVT)
D. Avian leukosis virus (ALV)

Answer: A
Explanation: Marek's disease (caused by MDV, an alphaherpesvirus) presents with lymphomatous infiltration of nerves, viscera, and eyes. REV causes immunosuppression and tumors but not typically nerve enlargement. HVT is used as a vaccine. ALV causes lymphoid leukosis but not nerve lesions.

Parasitic Diseases

Question 11
A broiler flock exhibits bloody diarrhea and high mortality. Postmortem reveals cecal cores and hemorrhagic cecitis. Which Eimeria species is most likely?
A. Eimeria acervulina
B. Eimeria maxima
C. Eimeria tenella
D. Eimeria necatrix

Answer: C
Explanation: Eimeria tenella causes cecal coccidiosis with hemorrhage and cecal cores. E. acervulina causes duodenal lesions. E. maxima causes jejunal lesions. E. necatrix causes mid-intestinal lesions. For species identification and control, see Avian Coccidiosis: Eimeria Species Identification, Commercial Vaccines, and Anticoccidial Resistance in Broiler Flocks.

Question 12
Which of the following is the most common route of transmission for Histomonas meleagridis in turkeys?
A. Ingestion of embryonated eggs
B. Ingestion of Heterakis gallinarum eggs containing histomonads
C. Direct contact with infected birds
D. Aerosol inhalation

Answer: B
Explanation: Histomonas meleagridis is transmitted within the eggs of the cecal worm Heterakis gallinarum. Turkeys ingest the worm eggs, and histomonads are released in the ceca. Direct transmission is less efficient. Embryonated eggs are not the typical stage.

Question 13
A pigeon loft experiences high mortality with caseous oral plaques and necrotic ingluvitis. Wet mount of oral lesions shows flagellated protozoa. Which pathogen is responsible?
A. Trichomonas gallinae
B. Giardia duodenalis
C. Cryptosporidium baileyi
D. Plasmodium relictum

Answer: A
Explanation: Trichomonas gallinae causes avian trichomoniasis (canker) in pigeons and raptors, characterized by caseous oral and esophageal lesions. Giardia causes diarrhea. Cryptosporidium causes respiratory or intestinal disease. Plasmodium causes avian malaria. For diagnostic PCR panels, see Avian Trichomoniasis: Pathogenesis in Pigeons and Poultry, Diagnostic PCR Panels, and Control in Lofts and Flocks.

Question 14
Which of the following is the most effective method for diagnosing Ascaridia galli infection in a flock?
A. Fecal flotation with saturated salt solution
B. Direct smear of intestinal contents
C. ELISA for serum antibodies
D. PCR on blood samples

Answer: A
Explanation: Fecal flotation is the standard method for detecting Ascaridia galli eggs. Direct smear is less sensitive. ELISA is not routinely used. PCR on blood is not applicable as the parasite is intestinal.

Question 15
A layer flock shows decreased egg production and pale combs. Blood smear reveals large, pear-shaped protozoa within erythrocytes. Which parasite is most likely?
A. Leucocytozoon caulleryi
B. Plasmodium gallinaceum
C. Haemoproteus meleagridis
D. Babesia spp.

Answer: A
Explanation: Leucocytozoon species cause leucocytozoonosis in poultry, with schizonts in erythrocytes and leukocytes. Plasmodium causes avian malaria but is less common in chickens. Haemoproteus is more common in pigeons. Babesia is rare in poultry.

Fungal Diseases

Question 16
A group of 2-week-old poults presents with gasping, dyspnea, and high mortality. Postmortem shows yellow-white nodules in the lungs and air sacs. Which fungus is most likely?
A. Aspergillus fumigatus
B. Candida albicans
C. Mucor spp.
D. Histoplasma capsulatum

Answer: A
Explanation: Aspergillus fumigatus causes aspergillosis (brooder pneumonia) in young poultry, with characteristic granulomatous nodules in the respiratory tract. Candida causes thrush in the crop. Mucor is a rare opportunistic pathogen. Histoplasma is not a primary poultry pathogen.

Question 17
Which diagnostic method is most appropriate for confirming aspergillosis in a live bird?
A. Fungal culture of tracheal swab on Sabouraud dextrose agar
B. Direct microscopy of lung tissue with KOH
C. Serum galactomannan ELISA
D. PCR on air sac swab

Answer: D
Explanation: PCR on respiratory swabs provides rapid, specific detection of Aspergillus DNA. Culture is confirmatory but slow. KOH microscopy is less sensitive. Galactomannan ELISA is used in human medicine but not validated for poultry.

Question 18
A backyard chicken has white, raised plaques on the tongue and crop mucosa. Wet mount shows budding yeast cells with pseudohyphae. Which condition is this?
A. Candidiasis
B. Aspergillosis
C. Trichomoniasis
D. Vitamin A deficiency

Answer: A
Explanation: Candidiasis (crop mycosis) caused by Candida albicans presents with white plaques and pseudohyphae on microscopy. Trichomoniasis shows flagellated protozoa. Vitamin A deficiency causes hyperkeratosis but not yeast.

Differential Diagnosis Decision Tree

The following Mermaid diagram illustrates a decision tree for respiratory disease differential diagnosis in poultry based on clinical signs and gross lesions.

flowchart TD
    A[Respiratory signs in poultry], > B{Tracheal lesions?}
    B, >|Hemorrhagic tracheitis, plugs| C[Infectious laryngotracheitis]
    B, >|Mucoid exudate, ciliary loss| D[Infectious bronchitis]
    B, >|Caseous exudate, sinus swelling| E[Infectious coryza]
    B, >|No significant tracheal lesions| F{Systemic signs?}
    F, >|Neurologic signs, edema| G[Newcastle disease or HPAI]
    F, >|Sudden death, septicemia| H[Avian cholera]
    F, >|Mild respiratory, egg drop| I[Egg drop syndrome or low-path AI]

Summary Table of Key Poultry Pathogens

Conclusion

Self-assessment using MCQs is a valuable tool for mastering poultry disease diagnostics. The questions presented here cover the major bacterial, viral, parasitic, and fungal pathogens affecting poultry. Integration of clinical, pathological, and molecular diagnostic knowledge is essential for accurate diagnosis and effective control. Practitioners are encouraged to consult the referenced articles on this portal for deeper insights into specific pathogens and diagnostic techniques.

References

1. Swayne DE, Boulianne M, Logue CM, et al. Diseases of Poultry. 14th ed. Wiley-Blackwell; 2020.
2. Harrison GJ, Lightfoot TL. Clinical Avian Medicine. Spix Publishing; 2006.
3. Saif YM, Fadly AM, Glisson JR, et al. Diseases of Poultry. 12th ed. Blackwell Publishing; 2008.
4. McDougald LR. Coccidiosis. In: Swayne DE, ed. Diseases of Poultry. 14th ed. Wiley-Blackwell; 2020:1193-1225.
5. Charlton BR, Bermudez AJ, Boulianne M, et al. Avian Disease Manual. 7th ed. American Association of Avian Pathologists; 2015.